Biotechnology is a rapidly evolving field which is heavily dependent upon testing. Many of the procedures of interest in this field are outlined in U.S. Pat. No. 5,104,621 to Pfost et al. A common step in many of these procedures is fluid manipulation such as pipetting, diluting, dispensing and aspirating. Due to the extensive number of samples to be handled, the repetitive nature of the testing and the required precision, testing procedures are frequently automated. One device which is commonly used for the performance of fluid manipulation in an automated system is a multi-channel pipettor.
Multi-channel pipettors typically use pipette tips. In particular, disposable pipette tips provide several benefits such as minimizing the risk of cross-contamination of samples and allowing the use of tips of different sizes and shapes for different applications. However, when the multi-channel pipettor is incorporated into an automated system, problems unique to the process of fitting the multi-channel pipettor with the pipette tips arise.
Pipette tips are commonly provided in boxes for use with particular multi-channel pipettors. The boxes are normally injection molded to match the matrix pattern of the multichannel pipettor. One of the most common multi-channel pipettors is a 96 channel pipettor having a matrix of 8 channels by 12 channels on 9 mm centers. To frictionally fit the pipette tips onto the multi-channel pipettor, the box holding the pipette tips and mandrels are moved toward each other, usually so the mandrels are inserted into the interior channel of the pipette tips. The mandrels, with the attached pipette tips, are then moved away from the pipette tip box. Ideally, the slight weight of the pipette tip box, via gravity, is sufficient to prevent the pipette tip box from binding to the pipette tips.
In order for the above process to work, the clearance between the pipette tips and the box where the tip is supported has to be made to relatively strict specifications so that each pipette tip properly aligns with a mandrel. Any variation in the alignment between the tips and the mandrels is likely to create an imprecise mating when the two are forced together. Consequently, the tip would be seated with a slight misalignment to the mandrel. While the misalignment may not affect the eventual operation to be performed by the pipettor, any time a tip is misaligned the potential exists for the box to bind on the tips rather than falling away from the tips. In addition, binding between pipette tips and a pipette tip box can also be caused by the friction between the tips and box generated by the downward pressure generated by the mandrels being forced into the pipette tips to mount the pipette tips on the mandrels.
However, as the clearances are narrowed to ensure proper alignment, the allowed misalignment before binding occurs is also narrowed. This engineering problem is further complicated by the fact that manufacturing equipment settings will drift over time. Additionally, the curing process of injection molded items, such as pipette tips and boxes, can affect the tolerances for a particular batch of tips and boxes. This problem is further exacerbated due to the number of manufacturers for boxes, each having unique system errors for their manufacturing process.
Consequently, a common malfunction of an automated system incorporating a multichannel pipettor is for the pipette tip box to bind to the tips as the tips are forced onto the mandrels. Once the box binds, a variety of consequences may be realized when the multichannel pipettor moves the mandrels with the tip box unintentionally bound to the mandrels. For example, the system may stop, requiring the operator to handle potentially dangerous materials to reset the system. Alternatively, expensive components may be damaged or dangerous substances may be spilled or splashed.
Prior systems have attempted to address this problem by providing static shucker arms on a shucker plate, and, after pipette tips have been mounted on mandrels, partially retracting the mandrels. If the pipette box is bound to the pipette tips, the box will move upward with the pipette tips as they are partially retracted. The extent to which the mandrels are retracted is enough to cause the top of the pipette tip box to touch the shucker arms, but not enough to cause the pipette tips to engage the shucker plate, which would cause the pipette tips to be de-mounted from the mandrels. Unfortunately, this mere touching of the shucker arms by the upwardly moving pipette tip box is not sufficient to consistently ensure that sufficient force is imparted to the tip box by the shucker arms to dislodge the box from the pipette tips.
What is desired, therefore, is an apparatus and method for loading pipette tips onto pipettors which ensures that the tip box does not bind on the attached tips. The apparatus and method is preferably inexpensive to realize and compatible with existing pipettors and a variety of commercially available boxes. Finally, the apparatus and method should desirably have an extremely low failure rate.